What function does the TEST button serve for the reading lights?

The TEST button is specifically designed to ensure that both the passenger reading lights and the flight attendant call lights are functioning properly. When pressed, this button activates the lights momentarily, allowing crew members to verify that the illumination works correctly. This is crucial for safety and communication on board, ensuring that both passengers can read as needed and that flight attendants can be alerted effectively when assistance is required. By verifying the operation of these lights, crew members can address any issues before they impact service or safety during the flight.